The disease cysticercosis, caused by the larval form of Taenia solium, is endemic in all regions of the world where humans and pigs live in close contact. The lifecycle of T. solium begins when swine, the intermediate hosts, ingest tapeworm eggs excreted in the feces of a tapeworm carrier. The larvae hatch from the eggs and invade most tissues of the swine, giving rise to the disease cysticercosis.
When humans ingest raw or undercooked meat from cysticercotic swine, tapeworms, or taeniasis, develop. Patients with taeniasis may exhibit epigastric discomfort, nausea, irritability, diarrhea, and weight loss. In addition, proglottids, or individual segments of the tapeworm that are self-contained hermaphroditic reproductive units, may obstruct the appendix, biliary duct, or pancreatic duct.
Humans may also ingest T. solium eggs present in contaminated food and water and become infected with the larval form. After T. solium eggs are ingested, cysticerci may develop in the subcutaneous tissues, muscles, heart, lungs, liver, brain, and eye. Although small numbers of viable cysticerci may fail to produce symptoms in the infected host, death of the larvae stimulate a marked inflammatory reaction, fever, muscle pains, and eosinophilia. If the larvae invade the central nervous system, a single cyst may cause disease. The host may develop meningoencephalitis, epileptic seizures, dementia and other neurologic or psychiatric manifestations, and death can result from acute intracranial hypertension. The various manifestations of neurologic dysfunction caused by T. solium infection are collectively termed neurocysticercosis. T. solium neurocysticercosis has a current worldwide toll of 50 million cases with 50,000 deaths each year. Although neurocysticercosis is rarely acquired in the United States, it is common in Latin America, Asia, sub-Saharan Africa, and Eastern Europe. Due to the increased travel and immigration from highly endemic areas, detection and treatment of T. solium related diseases are U.S. public health priorities.
Diagnosis of cysticercosis historically relied on histological identification of the parasite by biopsy or autopsy. Although radiologic methods such as computed tomography or nuclear magnetic resonance imaging are useful in diagnosing neurocysticercosis, they are often too expensive or inaccessible in developing countries. In addition, although serological diagnostic tests are available to identify T. solium infection and diagnose neurocysticercosis, current immunoelectrotransfer blot (EITB) assays utilize purified, naturally-occurring T. solium larval proteins, making the assay reagents expensive and difficult to produce (see U.S. Pat. No. 5,354,660 to Tsang et al.).
In developing countries where T. solium related diseases are endemic, access to diagnostic assays can be limited due to the high cost of using T. solium antigens that are produced using complicated purification procedures. Furthermore, because cysticercosis is most prevalent in rural areas of developing countries, a field test is needed for epidemiological studies and surveillance. A field assay using inexpensive and reliable reagents would be an important tool in breaking the transmission cycle of the parasite, enabling the on-site diagnosis of infected pigs and immediate treatment with anti-helminthic agents such as oxfendazole. A field diagnosis of cysticercosis would also serve as an economic benefit to pig farmers, because uninfected pigs command a higher price.
Therefore, there is a need to clone the T. solium glycoproteins so that recombinant proteins can be readily produced for field testing and diagnosis of cysticercosis and neurocysticercosis.